Internal attentional window affects the processing of external stimuli depending on predictability.

Whereas external attention selects perceptual information, the selection of internal attention is based on internal representation in memory. Previous research has demonstrated that external and internal attention interact with each other. However, Lim and Pratt, Attention, Perception, & Psychophysics, 85, 52-63, (2023) reported that the breadth of the internal attentional window does not affect the processing of external perceptual stimuli. In that previous study, internal attention was manipulated by presenting a broad or narrow working memory array. While maintaining this array, participants performed a flanker task in which a distractor was presented at either far or near distances from the target. The results revealed no significant effect of the overlap between the internal attentional window and the external stimuli on participants' performance in the flanker task. However, the previous study varied the internal attentional window size and the flanker distance on a trial-to-trial basis, which may have prevented participants from maintaining the breadth of the internal attentional window. To investigate whether the breadth of the internal attentional window affects the processing of external stimuli under predictable attentional window breadth and flanker distance, we adopted the experimental paradigm of Lim and Pratt while keeping the internal attentional window breadth and the flanker distance consistent within a block. Our findings demonstrated that flanker processing was disrupted when the flanker fell within the breadth of the internal attentional window but only when the attentional window breadth was predictable. These findings suggest that internal attention affects processing of external stimuli when top-down knowledge of the task context is available.